Since the development of laser diodes, many applications for their use have been developed. Increasingly, laser diodes are employed for communications and are integral to optical disc recording and storage systems. Typically, edge emitting diode lasers are used. Edge emitting diode lasers, however, have a high cost in parallel and serial data links, and have a high current drain due to a high threshold current when used in compact disc pickups.
New systems are being developed to employ vertical cavity surface emitting lasers (VCSELs) in place of edge emitting lasers. The VCSELs provide a much lower cost, use surface emissions which simplify optical devices and are capable of being fabricated in larger volumes on semiconductor wafers. However, a problem exists in the packaging of such VCSELs, namely the cost of materials employed in the typical "can" type packages and the steps that must be taken for achieving proper alignment, more particularly z-axis alignment, of the laser chip within the package due to variations in the thickness of the actual laser chip, the semiconductor wafer, or the like and its dimensional reference to an optical element. In addition, there exists a need to integrate a collimating lens into the package, that again is aligned relative to the z-axis and a specific reference point, so as to allow for ease in fabrication, typically employing automated assembly.
The conventional semiconductor laser apparatus utilizes a metal TO can for packaging, and includes the formation of a "window" within a cap portion of the can through which the laser emission passes. The laser chip is positioned within the can based on measurements specific for that chip. This positioning allows for variation of the chip thickness, etc., yet is not time or cost effective. In addition, in the typical metal can a "window" must be formed to allow for the passage of the emission. An external lens will be placed in the light path away from the window typically for beam focusing and shaping. More specifically, in the prior art, the laser package is designed to focus the beam into a diffraction limited spot, and does not employ any collimating means. Due to poor die placement accuracy by automated machine, typically .+-.80 .mu.m, therefore manual z-axis alignment is needed to control the relative distance between the lens and the laser emission aperture. This procedure not only increases the system packaging cost, but also limits the manufacturing throughput.
In monitoring the power of these devices, generally, edge emitting laser diodes employ a power monitoring detector facing the back emission facet of the device. In a VCSEL with a wavelength shorter than 870 nm, there is no back emission due to the opaque substrate on which the device is necessarily formed. Accordingly, monitoring of the actual laser emission is required.
Therefore, there exists a need for improved packaging of vertical cavity surface emitting lasers, more specifically a package that utilizes existing leadframe technology, thus allowing for controlled alignment of the laser chip emission aperture along the z-axis, relative to an optical element, such as an integrated or separately formed collimating or focusing lens, so as to reduce the cost of manufacture and the complexity of system assembly. In addition, there is a need to incorporate into the package a monitoring system which will automatically control the emissions emitted by the VCSEL.
Thus there is a need for a lower cost semiconductor laser package that has included therein a leadframe, allowing for a means for aligning the laser chip so as to allow proper z-axis alignment of the laser emission aperture relative to an optical element, an optional power monitoring system, thus allowing for automatic power control (APC) of the VCSEL emission, which package utilizes low cost materials, and is simple to fabricate.
Accordingly, it is highly desirable and an object of this invention to provide for a low cost semiconductor laser package that incorporates proper z-axis alignment of the laser chip emission aperture relative to an optical element, such as a collimating lens.
It is another purpose of the present invention to provide for a new and improved semiconductor laser package that is fabricated using standard leadframe technology and molding techniques.
It is yet another purpose of the present invention to provide for a new and improved semiconductor laser package that is inexpensive and easily fabricated.
It is a still further purpose of the present invention to provide for a new and improved semiconductor laser package that allows for optional automatic power control of the VCSEL emission.